1. Field of the Invention
The present invention relates to a defect inspection apparatus and a defect inspection method.
2. Related Background Art
As the sizes of semiconductor patterns are becoming smaller in recent years, the sizes of defects that affect the performance of semiconductor products are also becoming smaller. Therefore, it is becoming more difficult to detect such minute-size defects with a conventional inspection apparatus. Most of the conventional inspection methods are based on a comparison between an inspection pattern and a reference pattern. Such conventional inspection methods include a die-to-die method involving a die as a reference pattern adjacent to an inspection pattern (see Japanese Patent Laid-Open Pub. No. 2002-365786, for example), and a die-to-database method involving design data as a reference pattern.
However, there are some problems with each of those methods.
For example, by the die-to-die method, an inspection cannot be performed if there are no chips having the same pattern, as disclosed in Japanese Patent Laid-Open Pub. No. 2002-365786. Even if there are chips having the same pattern, there are minute fluctuations in the pattern shape of each pattern due to uncontrollable process fluctuations such as roughness, thereby no two patterns are completely the same. Thus, it is difficult to distinguish defects from the minute changes when minute-size defects are to be detected. This is one of the reasons that pseudo defects are caused in defect inspections.
By the die-to-database method, on the other hand, a computer aided design (CAD) pattern is referred to. Though no minute fluctuations are caused in the reference pattern, there is normally a large difference in shape between a CAD pattern and an inspection pattern. As a result, pseudo defects also become a serious problem when minute-size defects are to be detected.
Furthermore, the die-to-die method and the die-to-database method share a common problem that a reference/comparison pattern needs to be obtained separately from an inspection pattern, or needs to be prepared in advance. Such a troublesome procedure leads to an increase in inspection time, and an increase in inspection costs.